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Revenue Disaggregation of Revenue (Details) - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | $ 2,101 | $ 2,347 | $ 2,249
At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 58 | 78 | 65
Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 965 | 990 | 1,096
Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 1,023 | 1,068 | 1,161
Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 123 | 130 | 170
Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 407 | 296 | 165
Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 5 | 8 | 16
Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 543 | 845 | 737
Hydro | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 152 | 156 | 156
Hydro | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Hydro | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 141 | 142 | 132
Hydro | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 141 | 142 | 132
Hydro | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 7
Hydro | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Hydro | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 1 | 0 | 0
Hydro | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 10 | 14 | 17
Wind and Solar | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 329 | 312 | 282
Wind and Solar | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 25 | 27 | 18
Wind and Solar | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 236 | 217 | 188
Wind and Solar | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 261 | 244 | 206
Wind and Solar | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 27
Wind and Solar | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | (2) | 18 | (20)
Wind and Solar | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 4 | 8 | 16
Wind and Solar | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 66 | 42 | 53
North American Gas | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 217 | 209 | 232
North American Gas | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
North American Gas | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 196 | 190 | 206
North American Gas | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 196 | 190 | 206
North American Gas | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 8 | 0 | 0
North American Gas | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 4 | 2 | 4
North American Gas | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
North American Gas | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 9 | 17 | 22
Australian Gas | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 158 | 160 | 165
Australian Gas | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Australian Gas | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 90 | 87 | 91
Australian Gas | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 90 | 87 | 91
Australian Gas | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 60 | 65 | 68
Australian Gas | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Australian Gas | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Australian Gas | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 8 | 8 | 6
Alberta Thermal | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 619 | 816 | 912
Alberta Thermal | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 23 | 41 | 38
Alberta Thermal | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 302 | 354 | 479
Alberta Thermal | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 325 | 395 | 517
Alberta Thermal | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 55 | 65 | 68
Alberta Thermal | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | (12) | (17) | (1)
Alberta Thermal | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Alberta Thermal | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 251 | 373 | 328
Centralia | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 497 | 571 | 442
Centralia | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 10 | 10 | 9
Centralia | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Centralia | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 10 | 10 | 9
Centralia | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Centralia | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 283 | 160 | 115
Centralia | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Centralia | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 204 | 401 | 318
Energy Marketing | Operating segments |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 122 | 129 | 67
Energy Marketing | Operating segments | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 122 | 129 | 67
Energy Marketing | Operating segments | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Energy Marketing | Operating segments | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate and Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 7 | (6) | (7)
Corporate and Other | At a point in time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate and Other | Over time |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate and Other | Contract With Customers |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate and Other | Lease Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate and Other | Derivatives Income |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 12 | 4 | 0
Corporate and Other | Government incentives |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | 0 | 0 | 0
Corporate and Other | Other |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Revenues | $ (5) | $ (10) | $ (7)

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